Method of and device for testing hermetically enclosed reed contacts

Abstract

Method of and apparatus for testing magnetostrictive reed contacts for poorly conductive surface contamination. The reed contact is closed in a magnetic field generated by a direct current. An alternating current is conducted through the closed reed contact, the frequency sweeping through the torsional resonant frequency of the contact reeds. The tested contact surface of the contact reeds is thus maximized. The voltage generated across the reed contact by the alternating current is then measured.

What is claimed is: 
     
       1. A method of testing contact surfaces of reed switches having electrically conductive contact reeds comprising a magnetostrictive material and susceptible to torsional movement upon application of a magnetic field by a coil within which the switch is located, comprising applying an excitation current which is a direct current to said coil so as to close contacts of said switch,   applying an alternating test current through said closed contacts, and   continuously varying the frequency of said test current between a minimum value less than a torsional resonant frequency of said contact and a maximum value greater than said torsional resonant frequency.   
     
     
       2. A method as claimed in claim 1 wherein said excitation current has a value which is a given constant percentage greater than a de-energizing direct current at which the reed contact under test changes from a closed to an open position. 
     
     
       3. A method as claimed in claim 1 wherein said excitation current has a de-energizing value at which the reed contact under test changes from a closed to an open position, said method comprising in addition the sequential steps of activating the coil with an excitation current of first value such that the magnetostrictive material is magnetically saturated, reducing said excitation current from said first value to a second value greater than said de-energizing value,   reducing said excitation current monotonically with time to said de-energizing value.   storing said value of de-energizing current,   again activating the coil with an excitation current sufficient to magnetically saturate said magentostrictive material, and   reducing the excitation current to a third value having a given constant percentage greater than said de-energizing value, said third being said direct current excitation current.   
     
     
       4. A method as claimed in claim 1 comprising applying a vibrating current to said coil before said excitation current, said vibrating current having a frequency less than the bending resonant frequency of the reed, the vibrating current producing a square wave magentic field intensity so as to open and close said contacts. 
     
     
       5. A method as claimed in claim 4 wherein said vibrating current is maintained such that said reed contact is closed and opened at least 10,000 times. 
     
     
       6. A method as claimed in claim 1 wherein said applying of vibrating current is preceded by the step of applying a switching current to said coil, said switching current having a direct current component and an alternating current component superimposed thereon, the alternating current having a frequency substantially equal to the bending resonant frequency of the reeds and a peak value less than the direct current component. 
     
     
       7. A testing device for reed switches, comprising a coil, power supply means for exciting the coil, a generator for generating a test current, means for conducting said test current to contacts to be tested, and detection means for detecting poor contact between said contacts, wherein said generator comprises a voltage controlled oscillator and said detection means comprises a bi-directional limit value detector. 
     
     
       8. A device as claimed in claim 7, comprising in addition a control unit, and wherein said power supply means comprises two independent supply section means controlled by said control unit for generating in succession a squarewave excitation current which changes to a linearly decreasing excitation current which decreases to a minimum value at which a contact reed being tested just opens, and a second squarewave excitation current which changes to a constant excitation current having a value which exceeds said minimum value by a constant percentage, one of said supply section means generating the squarewave excitation currents and the other section generating the current which decreases and the constant current.